Foaming concentrates based on protein hydrolysate have been known and used since before 1940 for use as fire fighting agents, for crop protection and for a variety of other applications. Frequently, a specific end use application will require a foam which is copious and persistent. Such foams are commonly achieved by the addition of certain metal salts such as those of calcium, zinc, and iron. There are also foaming agents commercially available which produce stable foams persistent for up to several hours. Other ingredients are often added to impart shelf life stability, lower the freezing point, and/or to alter the viscosity.
In order to achieve additional persistence, beyond several hours, water soluble polymers (hydrocolloids) have been added to the concentrate. However, of those few polymers which are effective, most are reactive with the metal ions which are necessarily a part of the formulation. Additionally, the incorporation of a hydrocolloid into the concentrate in a sufficient amount to render the foam persistent for several days (without regard to any interactions with other constituents) increases the viscosity of the concentrate beyond any usefulness. Thus, there is no known prior art protein hydrolysate based foam concentrate containing an effective water soluble polymer which exhibits any practical storage stability. Furthermore, it has been generally regarded by those skilled in such art that a protein hydrolysate concentrate containing multivalent cations and an effective polymer is not practical.
In the past such polymers were premixed in water and added to a foam solution premix of the concentrate just prior to use. After premixing, the concentrate was further diluted for foam production. This two part mixing procedure was inefficient and complex.
For marketing purposes, it is highly desirable to produce a concentrate having the polymer contained therein. Such a product eliminates the end user having to perform the two part mixing procedure. The new concentrate described herein makes it possible to use a one part mixing technique such that the end user need only dilute the concentrate prior to foam production.
Commercially available foam concentrates based on protein hydrolysate are available for use at concentrations ranging from 3% to 6% in water by volume. Such commercial preparations may be used at slightly below or above these ranges depending on the application. The hydrolysates are derived from keratin type proteins which impart the necessary foamability. Collagen or albumin proteins can be cohydrolized or prehydrolized and added later for improved foam stability. Hydrolysis can be accomplished by the use of mineral acids or strong bases, but alkaline hydrolysis with lime has been generally preferred. Subsequent neutralization with sulfuric acid and filtration to remove calcium sulfate renders the clear hydrolysate which may be concentrated to a desired gravity by evaporation. Other desired ingredients are then subsequently added.
Foamability is achieved to a large degree by the formation of surface active complexes by the association of protein liquids with metal cations such as Ca++, Zn++, Fe++, Fe+++. There are undisclosed amounts of residual Ca++ from the lime hydrolysis but formulations usually have additional ions added to achieve the desired effects. Coupling agents such as glycols, and glycol ethers are often added to enhance foamability. Within the described technology, foams have been made to persist up to 36 hours in some cases.
Other technologies utilizing synthetic surfactants in combinations with hydrocolloids such as polysaccarides are known for producing copious stable foams. But there is no established prior art foam demonstrating foam persistence for several days which can be made available in a practical and stable foam concentrate.